Stalk borers are hatching

Stalk borer hatching is in progress in southern Iowa and will commence by the middle of May in northern Iowa. Stalk borers begin hatching at 575 degree days (base 41° F) and are mostly done hatching at 750 degree days.

Continuous corn fields that historically have had serious stand loss problems from stalk borers should be scouted when corn emerges. In very young corn, stalk borers can be seen feeding and resting down inside the whorl. If the population exceeds the economic threshold, then an insecticide is warranted to prevent economic yield loss. Additional information on stalk borers is available in an Iowa State University Extension publication, Stalk borer ecology and pest management options in corn and soybeans, IPM-41.

Labeled insecticides and rates per acre include Ambush 2E (6.4-12.8 ounces), Asana XL (5.8-9.6 ounces), Lorsban 4E (2-3 pints), Pounce 3.2EC (4-8 ounces), or Warrior 1EC (2.56-3.84 ounces). Always read and follow label directions.

Stalk borer development: degree day accumulations base 41°F, January 1, 1997 through May 11, 1997.

Stalk borer economic thresholds.

Percent infested plants at four corn prices

Leaf stage $2/bu. $3/bu. $4/bu. $5/bu.
1 10% 7% 5% 4%
2 12% 8% 6% 5%
3 15% 10% 7% 6%
4 16% 11% 8% 6%
5 17% 12% 9% 7%
6 34% 23% 17% 14%
7 100% 100% 100% 100%

This article originally appeared on pages 66-67 of the IC-478 (9) -- May 19, 1997 issue.

Updated 05/18/1997 - 1:00pm